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Lehninger Principles of Biochemistry 7th Edition Nelson Test Bank
1. Which of the following statements about the fixation of atmospheric nitrogen (N2) into NH3 by living cells is false? A) It involves the transfer of e... [Show More] ight electrons per mol of N2. B) It occurs in certain microorganisms, but not in humans. C) It requires a source of electrons, normally ferredoxin. D) It requires one ATP per mol of N2 fixed. E) It requires two key protein components, each containing iron. D 2. Which of the following is not true about the anammox reaction? A) Anammox converts ammonia to nitrogen. B) Anammox is performed by symbiotic bacteria of leguminous plants. C) Anammox generates the highly reactive molecule hydrazine that is a component of rocket fuel. D) Anammox occursw anaerobically. E) The ultimate electron acceptor in anammox is nitrite. B 3. Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule? A) Dinitrogenase reductase B) Nitrate reductase C) Nitrite reductase D) Nitrile reductase E) Dinitrogenase D 4. Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule? A) Arginase B) Glutamate dehydrogenase C) Glutamate synthase D) Glutamine synthetase E) Dinitrogenase A 5. The enzymatic machinery to fix atmospheric N2 into NH4+ is: A) a means of producing ATP when excess N2 is available. B) composed of two key proteins, each containing iron. C) relatively stable when exposed to O2. D) specific to plant cells. E) unaffected by the supply of electrons. B 6. Glutamine synthetase converts _____ to _____ whereas glutamate synthase converts ____ to _____. A) formate; glutamine; ammonia; glutamate B) asparagine; glutamine; -ketoglutarate; glutamate C) alpha-ketoglutarate; glutamine; oxaloacetic acid; glutamate D) alpha-ketoglutarate; glutamine; alpha-ketoglutarate; glutamate E) glutamate; glutamine; alpha-ketoglutarate; glutamate E 7. Which of the following is not true about glutamine amidotransferases? A) These enzymes proceed via a covalent intermediate. B) Ammonia is released into a channel. C) Glutamate is a product of the reaction. D) ATP is needed to activate the glutamine. E) A Cys at the active site is critical for the activity of these enzymes. D 8. Nonessential amino acids: A) are amino acids other than those required for protein synthesis. B) are not utilized in mammalian proteins. C) are synthesized by plants and bacteria, but not by humans. D) can be synthesized in humans as well as in bacteria. E) may be substituted with other amino acids in proteins. D 9. An amino acid that does not derive its carbon skeleton, at least in part, from alpha-ketoglutarate is: A) arginine. B) glutamate. C) glutamine. D) proline. E) threonine. E 10. Glutamine, arginine, and proline: A) do not have a common precursor. B) may all be derived from a citric acid cycle intermediate. C) may all be derived from a Cori cycle intermediate. D) may all be derived from a glycolytic intermediate. E) may all be derived from a urea cycle intermediate. B 11. In which group are all the amino acids closely interrelated metabolically? A) Arginine, hydroxyproline, and histidine B) Arginine, tyrosine, and glutamate C) Glycine, valine, glutamine, and aspartate D) Ornithine, alanine, glycine, and valine E) Ornithine, proline, arginine, and glutamate E 12. If glucose labeled with 14C at C-1 were the starting material for amino acid biosynthesis, the product(s) that would be readily formed is (are): A) serine labeled at the carboxyl carbon. B) serine labeled at alpha carbon. C) serine labeled at the R-group carbon. D) All of the above E) None of the above C 13. An amino acid that does not derive its carbon skeleton, at least in part, from oxaloacetate is: A) aspartate. B) lysine. C) methionine. D) proline. E) threonine. D 14. Homoserine is: A) a precursor of both methionine and threonine. B) a precursor of serine. C) derived from homocysteine. D) derived from serine. E) derived from threonine. A 15. If a cell were unable to synthesize or obtain tetrahydrofolic acid (H4 folate), it would probably be deficient in the biosynthesis of: A) isoleucine. B) leucine. C) lysine. D) methionine. E) serine. D 16. The nitrogen atom in the side chain of lysine is derived from which amino acid? A) Aspartic acid B) Glutamic acid C) Glutamine D) Asparagine E) Arginine B 17. The nitrogen atom in the indole ring of tryptophan is derived from which amino acid? A) Aspartic acid B) Glutamic acid C) Glutamine D) Asparagine E) Arginine C 18. Erythrose 4-phosphate is a precursor of: A) aspartate. B) cysteine. C) phenylalanine. D) serine. E) threonine. C 19. An important intermediate in the biosynthetic pathway to aromatic amino acids is: A) benzoic acid. B) lactate. C) orotate. D) shikimate. E) alpha-ketoglutarate. D 20. Which of the following amino acids derives its nitrogen from a purine ring? A) Histidine B) Lysine C) Arginine D) Glutamine E) Tryptophan A 21. The amino acid__________ and is an intermediate in the biosynthesis of _________. A) histidine; purines B) glycine; heme C) serine; heme D) serine; sphingosine E) glutamine; glutathione B 22. Bile pigments are: A) formed in the degradation of heme. B) generated by oxidation of sterols. C) responsible for light reception in the vertebrate eye. D) secreted from the pancreas E) the products of purine degradation. A 23. Glutathione is a(n): A) enzyme essential in the synthesis of glutamate. B) isomer of oxidized glutamic acid. C) methyl-group donor in many biosynthetic pathways. D) product of glutamate and methionine. E) tripeptide of glycine, glutamate, and cysteine. E 24. The plant hormone indole-3-acetate (auxin) is formed from: A) arginine. B) histidine. C) phenylalanine. D) threonine. E) tryptophan. E 25. L-Dopa is an intermediate in the conversion of: A) phenylalanine to homogentisic acid. B) phenylalanine to tyrosine. C) tyrosine to epinephrine. D) tyrosine to phenylalanine. E) tyrosine to phenylpyruvate. C 26. The amino acid that gives rise to the biological messenger NO is: A) glutamine. B) arginine. C) proline. D) lysine. E) histidine. B 27. The hormones epinephrine and norepinephrine are derived biosynthetically from: A) arginine. B) histidine. C) isoleucine. D) tryptophan. E) tyrosine. E 28. One amino acid directly involved in the purine biosynthetic pathway is: A) alanine. B) aspartate. C) glutamate. D) leucine. E) tryptophan B 29. 5-Phosphoribosyl-alpha-pyrophosphate (PRPP) is a synthetic precursor for all of the following except: A) AMP. B) arginine. C) histidine. D) tryptophan. E) UMP. B 30. Glutamine is a nitrogen donor in the synthesis of: A) CTP. B) dTTP. C) inosinic acid (IMP). D) orotate. E) UMP. C 31. De novo purine biosynthesis is distinguished from de novo pyrimidine biosynthesis by: A) condensation of the completed purine ring with ribose phosphate B) incorporation of CO2. C) inhibition by azaserine (a glutamine analog). D) participation of aspartate. E) participation of PRPP (phosphoribosyl pyrophosphate). B 32. The ribosyl phosphate moiety needed for the synthesis of orotidylate, inosinate, and guanylate is provided most directly by: A) 5-phosphoribosyl 1-pyrophosphate. B) adenosine 5'-phosphate. C) guanosine 5'-phosphate. D) ribose 5-phosphate. E) ribulose 5-phosphate. A 33. The synthesis of purine and pyrimidine nucleotides differ in that: A) ATP is required in the synthesis of purines but not in the synthesis of pyrimidines. B) purine biosynthesis starts with the formation of PRPP, whereas pyrimidines incorporate the PRPP near the end of the pathway. C) purine formation requires a THF derivative, whereas pyrimidine formation does not. D) pyrimidine biosynthesis is tightly regulated in the cell, whereas purine biosynthesis is not. E) pyrimidines go through many steps, adding a single carbon or nitrogen each time, whereas the basic skeleton for purines is formed by two main precursors. B 34. Which one of the following statements is true of the biosynthetic pathway for purine nucleotides? A) CO2 does not participate in any of the steps in this pathway. B) Deoxyribonucleotides are formed from 5-phosphodeoxyribosyl 1-pyrophosphate. C) Inosinate is the purine nucleotide that is the precursor of both adenylate and guanylate. D) Orotic acid is an essential precursor for purine nucleotides. E) The amino acid valine is one of the precursors contributing to purine nucleotides. C [Show Less]
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Lehninger Principles of Biochemistry 7th Edition Nelson Test Bank
The chirality of an amino acid results from the fact that its α carbon: A) has no net charge. B) is a carboxylic acid. C) is bonded to four different c... [Show More] hemical groups. D) is in the L absolute configuration in naturally occurring proteins. E) is symmetric. C) is bonded to four different chemical groups. Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________. A) alanine; is a simple methyl group B) glycine; is a hydrogen atom C) glycine; is unbranched D) lysine; contains only nitrogen E) proline; forms a covalent bond with the amino group B) glycine; is a hydrogen atom Two amino acids of the standard 20 contain sulfur atoms. They are: A) cysteine and serine. B) cysteine and threonine. C) methionine and cysteine D) methionine and serine E) threonine and serine. C) methionine and cysteine All of the amino acids that are found in proteins, except for proline, contain a(n): A) amino group. B) carbonyl group. C) carboxyl group. D) ester group. E) thiol group. A) amino group. Which of the following statements about aromatic amino acids is correct? A) All are strongly hydrophilic. B) Histidine's ring structure results in its being categorized as aromatic or basic, depending on pH. C) On a molar basis, tryptophan absorbs more ultraviolet light than tyrosine. D) The major contribution to the characteristic absorption of light at 280 nm by proteins is the phenylalanine R group. E) The presence of a ring structure in its R group determines whether or not an amino acid is aromatic. C) On a molar basis, tryptophan absorbs more ultraviolet light than tyrosine. Which of the following statements about cystine is correct? A) Cystine forms when the —CH2—SH R group is oxidized to form a —CH2—S—S—CH2— disulfide bridge between two cysteines. B) Cystine is an example of a nonstandard amino acid, derived by linking two standard amino acids. C) Cystine is formed by the oxidation of the carboxylic acid group on cysteine. D) Cystine is formed through a peptide linkage between two cysteines. E) Two cystines are released when a —CH2—S—S—CH2— disulfide bridge is reduced to —CH2—SH. A) Cystine forms when the —CH2—SH R group is oxidized to form a —CH2—S—S—CH2— disulfide bridge between two cysteines. The uncommon amino acid selenocysteine has an R group with the structure —CH2—SeH (pKa ≈ 5). In an aqueous solution, pH = 7.0, selenocysteine would: A) be a fully ionized zwitterion with no net charge. B) be found in proteins as D-selenocysteine. C) never be found in a protein. D) be nonionic. E) not be optically active. A) be a fully ionized zwitterion with no net charge. Amino acids are ampholytes because they can function as either a(n): A) acid or a base. B) neutral molecule or an ion. C) polar or a nonpolar molecule. D) standard or a nonstandard monomer in proteins. E) transparent or a light-absorbing compound. A) acid or a base. Titration of valine by a strong base, for example NaOH, reveals two pK's. The titration reaction occurring at pK2 (pK2 = 9.62) is: A) —COOH + OH− → —COO− + H2O. B) —COOH + —NH2 → —COO− + —NH2+. C) —COO− + —NH2+ → —COOH + —NH2. D) —NH3+ + OH− → —NH2 + H2O. E) —NH2 + OH− → —NH− + H2O. D) —NH3+ + OH− → —NH2 + H2O. In a highly basic solution, pH = 13, the dominant form of glycine is: A) NH2—CH2—COOH. B) NH2—CH2—COO−. C) NH2—CH3+—COO−. D) NH3+—CH2—COOH. E) NH3+—CH2—COO−. C) NH2—CH3+—COO−. For amino acids with neutral R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will have: A) a net negative charge. B) a net positive charge. C) no charged groups. D) no net charge. E) positive and negative charges in equal concentration. B) a net positive charge. At pH 7.0, converting a glutamic acid to γ-carboxyglutamate, will have what effect on the overall charge of the protein containing it? A) it will become more negative B) it will become more positive. C) it will stay the same. D) there is not enough information to answer the question. E) the answer depends on the salt concentration. A) it will become more negative At pH 7.0, converting a proline to hydroxyproline, will have what effect on the overall charge of the protein containing it? A) it will become more negative B) it will become more positive. C) it will stay the same. D) there is not enough information to answer the question. E) the answer depends on the salt concentration. C) it will stay the same. What is the approximate charge difference between glutamic acid and α-ketoglutarate at pH 9.5? A) 0 B) ½ C) 1 D) 1½ E) 2 B) ½ The formation of a peptide bond between two amino acids is an example of a(n) ______________ reaction. A) cleavage B) condensation C) group transfer D) isomerization E) oxidation reduction B) condensation The peptide alanylglutamylglycylalanylleucine has: A) a disulfide bridge. B) five peptide bonds. C) four peptide bonds. D) no free carboxyl group. E) two free amino groups. C) four peptide bonds. An octapeptide composed of four repeating glycylalanyl units has: A) one free amino group on an alanyl residue. B) one free amino group on an alanyl residue and one free carboxyl group on a glycyl residue. C) one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue. D) two free amino and two free carboxyl groups. E) two free carboxyl groups, both on glycyl residues. C) one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue. At the isoelectric pH of a tetrapeptide: A) only the amino and carboxyl termini contribute charge. B) the amino and carboxyl termini are not charged. C) the total net charge is zero. D) there are four ionic charges. E) two internal amino acids of the tetrapeptide cannot have ionizable R groups. C) the total net charge is zero. Which of the following is correct with respect to the amino acid composition of proteins? A) Larger proteins have a more uniform distribution of amino acids than smaller proteins. B) Proteins contain at least one each of the 20 different standard amino acids. C) Proteins with different functions usually differ significantly in their amino acid composition. D) Proteins with the same molecular weight have the same amino acid composition. E) The average molecular weight of an amino acid in a protein increases with the size of the protein. C) Proteins with different functions usually differ significantly in their amino acid composition. The average molecular weight of the 20 standard amino acids is 138, but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight. Why? A) The number 110 is based on the fact that the average molecular weight of a protein is 110,000 with an average of 1,000 amino acids. B) The number 110 reflects the higher proportion of small amino acids in proteins, as well as the loss of water when the peptide bond forms. C) The number 110 reflects the number of amino acids found in the typical small protein, and only small proteins have their molecular weight estimated this way. D) The number 110 takes into account the relatively small size of nonstandard amino acids. E) The number 138 represents the molecular weight of conjugated amino acids. B) The number 110 reflects the higher proportion of small amino acids in proteins, as well as the loss of water when the peptide bond forms. In a conjugated protein, a prosthetic group is: A) a fibrous region of a globular protein. B) a nonidentical subunit of a protein with many identical subunits. C) a part of the protein that is not composed of amino acids. D) a subunit of an oligomeric protein. E) synonymous with "protomer." C) a part of the protein that is not composed of amino acids. Prosthetic groups in the class of proteins known as glycoproteins are composed of: A) carbohydrates. B) flavin nucleotides. C) lipids. D) metals . E) phosphates. A) carbohydrates. For the study of a protein in detail, an effort is usually made to first: A) conjugate the protein to a known molecule. B) determine its amino acid composition. C) determine its amino acid sequence. D) determine its molecular weight. E) purify the protein. A) conjugate the protein to a known molecule. In a mixture of the five proteins listed below, which should elute second in size-exclusion (gel- filtration) chromatography? A) cytochrome c Mr = 13,000 B) immunoglobulin G Mr = 145,000 C) ribonuclease A Mr = 13,700 D) RNA polymerase Mr = 450,000 E) serum albumin Mr = 68,500 B) immunoglobulin G Mr = 145,000 By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to: A) determine a protein's isoelectric point. B) determine an enzyme's specific activity. C) determine the amino acid composition of the protein. D) preserve a protein's native structure and biological activity. E) separate proteins exclusively on the basis of molecular weight. E) separate proteins exclusively on the basis of molecular weight. To determine the isoelectric point of a protein, first establish that a gel: A) contains a denaturing detergent that can distribute uniform negative charges over the protein's surface. B) exhibits a stable pH gradient when ampholytes become distributed in an electric field. C) is washed with an antibody specific to the protein of interest. D) neutralizes all ionic groups on a protein by titrating them with strong bases. E) relates the unknown protein to a series of protein markers with known molecular weights, Mr. B) exhibits a stable pH gradient when ampholytes become distributed in an electric field. The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a strip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step: A) proteins with similar isoelectric points become further separated according to their molecular weights. B) the individual bands become stained so that the isoelectric focus pattern can be visualized. C) the individual bands become visualized by interacting with protein-specific antibodies in the second gel. D) the individual bands undergo a second, more intense isoelectric focusing. E) the proteins in the bands separate more completely because the second electric current is in the opposite polarity to the first current. A) proteins with similar isoelectric points become further separated according to their molecular weights. The term specific activity differs from the term activity in that specific activity: A) is measured only under optimal conditions. B) is the activity (enzyme units) in a milligram of protein. C) is the activity (enzyme units) of a specific protein. D) refers only to a purified protein. E) refers to proteins other than enzymes. B) is the activity (enzyme units) in a milligram of protein. Which of the following refers to particularly stable arrangements of amino acid residues in a protein that give rise to recurring patterns? A) Primary structure B) Secondary structure C) Tertiary structure D) Quaternary structure E) None of the above B) Secondary structure Which of the following describes the overall three-dimensional folding of a polypeptide? A) Primary structure B) Secondary structure C) Tertiary structure D) Quaternary structure E) None of the above D) Quaternary structure The functional differences, as well as differences in three-dimensional structures, between two different enzymes from E. coli result directly from their different: A) affinities for ATP. B) amino acid sequences. C) roles in DNA metabolism. D) roles in the metabolism of E. coli. E) secondary structures. B) amino acid sequences One method used to prevent disulfide bond interference with protein sequencing procedures is: A) cleaving proteins with proteases that specifically recognize disulfide bonds. B) protecting the disulfide bridge against spontaneous reduction to cysteinyl sulfhydryl groups. C) reducing disulfide bridges and preventing their re-formation by further modifying the —SH groups. D) removing cystines from protein sequences by proteolytic cleavage. E) sequencing proteins that do not contain cysteinyl residues. C) reducing disulfide bridges and preventing their re-formation by further modifying the —SH groups. [Show Less]
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Lehninger Principles of Biochemistry 7th Edition Nelson Test Bank
1. Which of the following is not true of the reaction catalyzed by the pyruvate dehydrogenase complex? A) Biotin participates in the decarboxylation. B... [Show More] ) Both NAD+ and a flavin nucleotide act as electron carriers. C) The reaction occurs in the mitochondrial matrix. D) The substrate is held by the lipoyl-lysine "swinging arm." E) Two different cofactors containing —SH groups participate. A 2. Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA? A) ATP B) CoA-SH C) FAD D) Lipoic acid E) NAD+ A 3. Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA? A) Biotin, FAD, and TPP B) Biotin, NAD+, and FAD C) NAD+, biotin, and TPP D) Pyridoxal phosphate, FAD, and lipoic acid E) TPP, lipoic acid, and NAD+ E 4. Which of the following statements about the oxidative decarboxylation of pyruvate in aerobic conditions in animal cells is correct? A) One of the products of the reactions of the pyruvate dehydrogenase complex is a thioester of acetate. B) The methyl (—CH3) group is eliminated as CO2. C) The process occurs in the cytosolic compartment of the cell. D) The pyruvate dehydrogenase complex uses all of the following as cofactors: NAD+, lipoic acid, pyridoxal phosphate (PLP), and FAD. E) The reaction is so important to energy production that pyruvate dehydrogenase operates at full speed under all conditions. A 5. Glucose labeled with 14C in C-3 and C-4 is completely converted to acetyl-CoA via glycolysis and the pyruvate dehydrogenase complex. What percentage of the acetyl-CoA molecules formed will be labeled with 14C, and in which position of the acetyl moiety will the 14C label be found? A) 100% of the acetyl-CoA will be labeled at C-1 (carboxyl). B) 100% of the acetyl-CoA will be labeled at C-2. C) 50% of the acetyl-CoA will be labeled, all at C-2 (methyl). D) No label will be found in the acetyl-CoA molecules. E) Not enough information is given to answer this question. D 6. Which of the following is not true of the citric acid cycle? A) All enzymes of the cycle are located in the cytoplasm, except succinate dehydrogenase, which is bound to the inner mitochondrial membrane. B) In the presence of malonate, one would expect succinate to accumulate. C) Oxaloacetate is used as a substrate but is not consumed in the cycle. D) Succinate dehydrogenase channels electrons directly into the electron transfer chain. E) The condensing enzyme is subject to allosteric regulation by ATP and NADH. A 7. Acetyl-CoA labeled with 14C in both of its acetate carbon atoms is incubated with unlabeled oxaloacetate and a crude tissue preparation capable of carrying out the reactions of the citric acid cycle. After one turn of the cycle, oxaloacetate would have 14C in: A) all four carbon atoms. B) no pattern that is predictable from the information provided. C) none of its carbon atoms. D) the keto carbon and one of the carboxyl carbons. E) the two carboxyl carbons. A 8. Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which of the following compounds would you expect to decrease in concentration? A) Citrate B) Fumarate C) Isocitrate D) Pyruvate E) Succinate B 9. Which of the following is not an intermediate of the citric acid cycle? A) Acetyl-CoA B) Citrate C) Oxaloacetate D) Succinyl-CoA E) Alpha-Ketoglutarate A 10. In mammals, each of the following occurs during the citric acid cycle except: A) formation of -ketoglutarate. B) generation of NADH and FADH2. C) metabolism of acetate to carbon dioxide and water. D) net synthesis of oxaloacetate from acetyl-CoA. E) oxidation of acetyl-CoA. D 11. Oxaloacetate uniformly labeled with 14C (i.e., with equal amounts of 14C in each of its carbon atoms) is condensed with unlabeled acetyl-CoA. After a single pass through the citric acid cycle back to oxaloacetate, what fraction of the original radioactivity will be found in the oxaloacetate? A) All B) 1/2 C) 1/3 D) 1/4 E) 3/4 B 12. Conversion of 1 mol of acetyl-CoA to 2 mol of CO2 and CoA via the citric acid cycle results in the net production of: A) 1 mol of citrate. B) 1 mol of FADH2. C) 1 mol of NADH. D) 1 mol of oxaloacetate. E) 7 mol of ATP. B 13. Which one of the following is not associated with the oxidation of substrates by the citric acid cycle? A) All of the below are involved. B) CO2 production C) Flavin reduction D) Lipoic acid present in some of the enzyme systems E) Pyridine nucleotide oxidation E 14. The two moles of CO2 produced in the first turn of the citric acid cycle have their origin in the: A) carboxyl and methylene carbons of oxaloacetate B) carboxyl group of acetate and a carboxyl group of oxaloacetate. C) carboxyl group of acetate and the keto group of oxaloacetate. D) two carbon atoms of acetate. E) two carboxyl groups derived from oxaloacetate. E 15. The oxidative decarboxylation of alpha-ketoglutarate proceeds by means of multistep reactions in which all but one of the following cofactors are required. Which one is not required? A) ATP B) Coenzyme A C) Lipoic acid D) NAD+ E) Thiamine pyrophosphate A 16. The reaction of the citric acid cycle that is most similar to the pyruvate dehydrogenase complex-catalyzed conversion of pyruvate to acetyl-CoA is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinyl-CoA to succinate. E) Alpha-ketoglutarate to succinyl-CoA. E 17. Which one of the following enzymatic activities would be decreased by thiamine deficiency? A) Fumarase B) Isocitrate dehydrogenase C) Malate dehydrogenase D) Succinate dehydrogenase E) Alpha-Ketoglutarate dehydrogenase complex E 18. The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP) by substrate level phosphorylation is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinate to fumarate. E) succinyl-CoA to succinate. E 19. The standard reduction potentials (E'°) for the following half reactions are given. Fumarate + 2H+ + 2e- -->succinate E'° = +0.031 V FAD + 2H+ + 2e- -->FADH2 E'° = -0.219 V If succinate, fumarate, FAD, and FADH2, all at l M concentrations, were mixed together in the presence of succinate dehydrogenase, which of the following would happen initially? A) Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced. B) Fumarate would become reduced; FADH2 would become oxidized. C) No reaction would occur because all reactants and products are already at their standard concentrations. D) Succinate would become oxidized; FAD would become reduced. E) Succinate would become oxidized; FADH2 would be unchanged because it is a cofactor, not a substrate. B 20. For the following reaction, delta G'° = 29.7 kJ/mol. L-Malate + NAD+ --> oxaloacetate + NADH + H+ The reaction as written: A) can never occur in a cell. B) can only occur in a cell if it is coupled to another reaction for which G'° is positive. C) can only occur in a cell in which NADH is converted to NAD+ by electron transport. D) may occur in cells at certain concentrations of substrate and product. E) would always proceed at a very slow rate D 21. All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD+ except the reaction catalyzed by: A) isocitrate dehydrogenase. B) malate dehydrogenase. C) pyruvate dehydrogenase D) succinate dehydrogenase. E) the alpha-ketoglutarate dehydrogenase complex. D 22. Which of the following cofactors is required for the conversion of succinate to fumarate in the citric acid cycle? A) ATP B) Biotin C) FAD D) NAD+ E) NADP+ C 23. In the citric acid cycle, a flavin coenzyme is required for: A) condensation of acetyl-CoA and oxaloacetate. B) oxidation of fumarate. C) oxidation of isocitrate. D) oxidation of malate. E) oxidation of succinate. E 24. Which of the following intermediates of the citric acid cycle is prochiral? A) Citrate B) Isocitrate C) Malate D) Oxaloacetate E) Succinate A 25. Anaplerotic reactions . A) produce oxaloacetate and malate to maintain constant levels of citric acid cycle intermediates B) produce biotin needed by pyruvate carboxylase C) recycle pantothenate used to make CoA D) produce pyruvate and citrate to maintain constant levels of citric acid cycle intermediates E) All of the above A 26. Intermediates in the citric acid cycle are used as precursors in the biosynthesis of: A) amino acids. B) nucleotides. C) fatty acids. D) sterols. E) All of the above E 27. The conversion of 1 mol of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the citric acid cycle also yields _____ mol of NADH, _____ mol of FADH2, and _____ mol of ATP (or GTP). A) 2; 2; 2 B) 3; 1; 1 C) 3; 2; 0 D) 4; 1; 1 E) 4; 2; 1 D 28. During the reaction of pyruvate carboxylase, CO2 is covalently attached to all the following except: A) phosphate. B) biotin. C) pyruvate. D) lysine. E) All of the above D 29. Entry of acetyl-CoA into the citric acid cycle is decreased when: A) [AMP] is high. B) NADH is rapidly oxidized through the respiratory chain. C) the ratio of [ATP]/[ADP] is low D) the ratio of [ATP]/[ADP] is high. E) the ratio of [NAD+]/[NADH] is high. D 30. Citrate synthase and the NAD+-specific isocitrate dehydrogenase are two key regulatory enzymes of the citric acid cycle. These enzymes are inhibited by: A) acetyl-CoA and fructose 6-phosphate. B) AMP and/or NAD+. C) AMP and/or NADH. D) ATP and/or NAD+. E) ATP and/or NADH. E 31. During seed germination, the glyoxylate pathway is important to plants because it enables them to: A) carry out the net synthesis of glucose from acetyl-CoA. B) form acetyl-CoA from malate. C) get rid of isocitrate formed from the aconitase reaction. D) obtain glyoxylate for cholesterol biosynthesis. E) obtain glyoxylate for pyrimidine synthesis. A 32. A function of the glyoxylate cycle, in conjunction with the citric acid cycle, is to accomplish the: A) complete oxidation of acetyl-CoA to CO2 plus reduced coenzymes. B) net conversion of lipid to carbohydrate. C) net synthesis of four-carbon dicarboxylic acids from acetyl-CoA. D) net synthesis of long-chain fatty acids from citric acid cycle intermediates. E) Both B and C are correct. E [Show Less]
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Lehninger Principles of Biochemistry 7th Edition Nelson Test Bank
1. Under which circumstances are amino acids not metabolized via oxidative degradation? A) Starvation B) Plants growing in nutrient-rich soils C) Norm... [Show More] al protein turnover D) A diet rich in proteins E) Uncontrolled diabetes B 2. Which of these is not a protease that acts in the small intestine? A) Chymotrypsin B) Elastase C) Enteropeptidase D) Secretin E) Trypsin D 3. In the digestion of protein that occurs in the small intestine, which enzyme is critical in the activation of zymogens? A) Enteropeptidase B) Hexokinase C) Papain D) Pepsin E) Secretin A 4. Which of the following is a zymogen that can be converted to an endopeptidase that hydrolyzes peptide bonds adjacent to Lys and Arg residues? A) Chymotrypsinogen B) Pepsin C) Pepsinogen D) Trypsin E) Trypsinogen E 5. In amino acid catabolism, the first reaction for many amino acids is a(n): A) decarboxylation requiring thiamine pyrophosphate (TPP). B) hydroxylation requiring NADPH and O2. C) oxidative deamination requiring NAD+. D) reduction requiring pyridoxal phosphate (PLP). E) transamination requiring pyridoxal phosphate (PLP). E 6. The coenzyme required for all transaminations is derived from: A) niacin. B) pyridoxine (vitamin B6). C) riboflavin. D) thiamin. E) vitamin B12. B 7. The coenzyme involved in a transaminase reaction is: A) biotin phosphate. B) lipoic acid. C) nicotinamide adenine dinucleotide phosphate (NADP+). D) pyridoxal phosphate (PLP). E) thiamine pyrophosphate (TPP). D 8. Transamination from alanine to alpha-ketoglutarate requires the coenzyme: A) biotin. B) NADH. C) No coenzyme is involved. D) pyridoxal phosphate (PLP). E) thiamine pyrophosphate (TPP). D 9. Which of the following reactions involving an amino acid cannot be catalyzed via a PLP-dependent mechanism? A) Hydrolysis B) Decarboxylation C) Racemization D) Transamination E) Transimination A 10. Which of the following is not true of the reaction catalyzed by glutamate dehydrogenase? A) It is similar to transamination in that it involves the coenzyme pyridoxal phosphate (PLP). B) NH4+ is produced. C) The enzyme can use either NAD+ or NADP+ as a cofactor. D) The enzyme is glutamate-specific, but the reaction is involved in oxidizing other amino acids. E) -Ketoglutarate is produced from an amino acid. A 11. Glutamate is metabolically converted to -ketoglutarate and NH4+ by a process described as: A) deamination. B) hydrolysis. C) oxidative deamination. D) reductive deamination. E) transamination. C 12. The conversion of glutamate to an alpha-ketoacid and NH4+: A) does not require any cofactors. B) is a reductive deamination. C) is accompanied by ATP hydrolysis catalyzed by the same enzyme. D) is catalyzed by glutamate dehydrogenase. E) requires ATP. D 13. Urea synthesis in mammals takes place primarily in tissues of the: A) brain. B) kidney. C) liver. D) skeletal muscle. E) small intestine. C 14. Which substance is not involved in the production of urea from NH4+ via the urea cycle? A) Aspartate B) ATP C) Carbamoyl phosphate D) Malate E) Ornithine D 15. Which of these directly donates a nitrogen atom for the formation of urea during the urea cycle? A) Adenine B) Aspartate C) Creatine D) Glutamate E) Ornithine B 16. Conversion of ornithine to citrulline is a step in the synthesis of: A) aspartate. B) carnitine. C) pyruvate. D) tyrosine. E) urea. E 17. In the urea cycle, ornithine transcarbamoylase catalyzes: A) cleavage of urea to ammonia. B) formation of citrulline from ornithine and another reactant. C) formation of ornithine from citrulline and another reactant. D) formation of urea from arginine. E) transamination of arginine. B 18. Which of the following statements is false in reference to the mammalian synthesis of urea? A) Krebs was a major contributor to the elucidation of the pathway involved. B) The amino acid arginine is the immediate precursor to urea. C) The carbon atom of urea is derived from mitochondrial HCO3-. D) The precursor to one of the nitrogens of urea is aspartate. E) The process of urea production is an energy-yielding series of reactions. E 19. Which of the following amino acids are essential for humans? A) Alanine B) Aspartic acid C) Asparagine D) Serine E) Threonine E 20. If a person's urine contains unusually high concentrations of urea, which one of the following diets has he or she probably been eating recently? A) High carbohydrate, very low protein B) Very high carbohydrate, no protein, no fat C) Very very high fat, high carbohydrate, no protein D) Very high fat, very low protein E) Very low carbohydrate, very high protein E 21. Which of these amino acids can be directly converted into a citric acid cycle intermediate by transamination? A) Glutamic acid B) Serine C) Threonine D) Tyrosine E) Proline A 22. Which of these amino acids are both ketogenic and glucogenic? 1. Isoleucine 2. Valine 3. Histidine 4. Arginine 5. Tyrosine A) 1 and 5 B) 1, 3, and 5 C) 2 and 4 D) 2, 3, and 4 E) 2, 4, and 5 A 23. Tetrahydrofolate (THF) and its derivatives shuttle between different substrates. A) electrons B) H+ C) acyl groups D) one carbon units E) NH2 groups D 24. Which of the following is not a form of the most oxidized state of tetrahydrofolate (THF)? A) N10-formyl THF B) N5N10-methenyl THF C) N5N10-methylene THF D) N5-formyl THF E) N5-formimino THF C 25. The amino acids serine, alanine, and cysteine can be catabolized to yield: A) fumarate. B) pyruvate. C) succinate. D) alpha-ketoglutarate. E) None of the above B 26. Serine or cysteine may enter the citric acid cycle as acetyl-CoA after conversion to: A) oxaloacetate. B) propionate. C) pyruvate. D) succinate. E) succinyl-CoA. C 27. The human genetic disease phenylketonuria (PKU) can result from: A) deficiency of protein in the diet. B) inability to catabolize ketone bodies. C) inability to convert phenylalanine to tyrosine. D) inability to synthesize phenylalanine. E) production of enzymes containing no phenylalanine. C 28. In the human genetic disease maple syrup urine disease, the metabolic defect involves: A) a deficiency of the vitamin niacin. B) oxidative decarboxylation. C) synthesis of branched chain amino acids. D) transamination of an amino acid. E) uptake of branched chain amino acids into liver. B [Show Less]
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Lehninger Principles of Biochemistry 7th Edition Nelson Test Bank
1. If the delta G'° of the reaction A --> B is -40 kJ/mol, under standard conditions the reaction: A) is at equilibrium. B) will never reach equilibri... [Show More] um. C) will not occur spontaneously. D) will proceed at a rapid rate. E) will proceed spontaneously from A to B. E For the reaction A --->B, delta G'° = -60 kJ/mol. The reaction is started with 10 mmol of A; no B is initially present. After 24 hours, analysis reveals the presence of 2 mmol of B, 8 mmol of A. Which is the most likely explanation? A) A and B have reached equilibrium concentrations. B) An enzyme has shifted the equilibrium toward A. C) B formation is kinetically slow; equilibrium has not been reached by 24 hours. D) Formation of B is thermodynamically unfavorable. E) The result described is impossible, given the fact thatG'° is -60 kJ/mol. C The reaction A + B --->C has a delta G'° of -20 kJ/mol at 25° C. Starting under standard conditions, one can predict that: A) at equilibrium, the concentration of B will exceed the concentration of A. B) at equilibrium, the concentration of C will be less than the concentration of A. C) at equilibrium, the concentration of C will be much greater than the concentration of A or B. D) C will rapidly break down to A + B. E) when A and B are mixed, the reaction will proceed rapidly toward formation of C. C Which of the following compounds has the largest negative value for the standard free-energy change (G'°) upon hydrolysis? A) Acetic anhydride B) Glucose 6-phosphate C) Glutamine D) Glycerol 3-phosphate E) Lactose A For the following reaction, delta G'° = +29.7 kJ/mol. L-Malate + NAD+ --->oxaloacetate + NADH + H+ The reaction as written: A) can never occur in a cell. B) can occur in a cell only if it is coupled to another reaction for which delta G'° is positive. C) can occur only in a cell in which NADH is converted to NAD+ by electron transport. D) cannot occur because of its large activation energy. E) may occur in cells at some concentrations of substrate and product. E For the reaction A --->B, the Keq' is 104. If a reaction mixture originally contains 1 mmol of A and no B, which one of the following must be true? A) At equilibrium, there will be far more B than A. B) The rate of the reaction is very slow. C) The reaction requires coupling to an exergonic reaction in order to proceed. D) The reaction will proceed toward B at a very high rate. E) Delta G'° for the reaction will be large and positive. A For the reaction A --->B, the Keq' is 10-6. If a reaction mixture originally contains 1 mmol of A and 1 mmol of B, which one of the following must be true? A) At equilibrium, there will be still be equal levels of A and B. B) The rate of the reaction is very slow. C) At equilibrium, the amount of A will greatly exceed the amount of B. D) The reaction will proceed toward B at a very high rate. E) Delta G'° for the reaction will be large and positive. A In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change (delta G'°) of 23.8 kJ/mol. Under what conditions encountered in a normal cell will the free-energy change (delta G) be negative, enabling the reaction to proceed spontaneously to the right? A) Under standard conditions, enough energy is released to drive the reaction to the right. B) The reaction will not go to the right spontaneously under any conditions because theG'° is positive. C) The reaction will proceed spontaneously to the right if there is a high concentration of products relative to the concentration of fructose 1,6-bisphosphate. D) The reaction will proceed spontaneously to the right if there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products. E) None of the above conditions is sufficient. A Which of the following is not nucleophilic? A) A proton B) A carbanion C) An imidazole D) A hydroxide E) A carboxylic acid A Which of the following is not electrophilic? A) A proton B) A sulfhydryl C) A protonated imine D) A carbonyl group E) A phosphoryl group B Which of the following is not true? A) The carbon adjacent to a carbonyl can be resonance stabilized to form a carbanion. B) A carbonyl carbon can be made more electrophilic by a nearby metal ion. C) The carbon adjacent to an imine can be resonance stabilized to form a carbanion D) Decarboxylation of an -keto acid goes through a carbocation intermediate. E) A Claisen ester condensation reaction goes through a carbanion intermediate. D The reaction ATP ---> ADP + Pi is an example of a_______reaction. A) homolytic cleavage B) internal rearrangement C) free radical D) group transfer E) oxidation/reduction D Which of the following is true about oxidation-reduction reactions? A) They usually proceed through homolytic cleavage. B) During oxidation a compound gains electrons. C) Dehydrogenases typically remove two electrons and two hydrides. D) There are four commonly accessed oxidation states of carbon. E) Every oxidation must be accompanied by a reduction. E All of the following contribute to the large, negative, free-energy change upon hydrolysis of "high-energy" compounds except: A) electrostatic repulsion in the reactant. B) low activation energy of forward reaction. C) stabilization of products by extra resonance forms. D) stabilization of products by ionization. E) stabilization of products by solvation. B The hydrolysis of ATP has a large negative delta G'°; nevertheless it is stable in solution due to: A) entropy stabilization. B) ionization of the phosphates. C) resonance stabilization. D) the hydrolysis reaction being endergonic. E) the hydrolysis reaction having a large activation energy. E The hydrolysis of phosphoenolpyruvate proceeds with a delta G'° of about -62 kJ/mol. The greatest contributing factors to this reaction are the destabilization of the reactants by electostatic repulsion and stabilization of the product pyruvate by: A) electrostatic attraction. B) ionization. C) polarization. D) resonance. E) tautomerization. E Which one of the following compounds does not have a large negative free energy of hydrolysis? A) 1,3-bis phosphoglycerate B) 3-phosphoglycerate C) ADP D) Phosphoenolpyruvate E) Thioesters (e.g. acetyl-CoA) B The immediate precursors of DNA and RNA synthesis in the cell all contain: A) 3' triphosphates. B) 5' triphosphates. C) adenine. D) deoxyribose. E) ribose. B Muscle contraction involves the conversion of: A) chemical energy to kinetic energy. B) chemical energy to potential energy. C) kinetic energy to chemical energy. D) potential energy to chemical energy. E) potential energy to kinetic energy. A Biological oxidation-reduction reactions always involve: A) direct participation of oxygen. B) formation of water. C) mitochondria. D) transfer of electron(s). E) transfer of hydrogens. D Biological oxidation-reduction reactions never involve: A) transfer of e- from one molecule to another. B) formation of free e-. C) transfer of H+ (or H3O+) from one molecule to another. D) formation of free H+ (or H3O+). E) none of the above. B The standard reduction potentials (E'°) for the following half reactions are given. Fumarate + 2H+ + 2e- --->succinate E'° = +0.031 V FAD + 2H+ + 2e- --->FADH2 E'° = -0.219 V If you mixed succinate, fumarate, FAD, and FADH2 together, all at l M concentrations and in the presence of succinate dehydrogenase, which of the following would happen initially? A) Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced. B) Fumarate would become reduced; FADH2 would become oxidized. C) No reaction would occur because all reactants and products are already at their standard concentrations. D) Succinate would become oxidized; FAD would become reduced. E) Succinate would become oxidized; FADH2 would be unchanged because it is a cofactor. B [Show Less]
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Lehninger Principles of Biochemistry 7th Edition Nelson Test Bank
Which of the following pairs of bonds within a peptide backbone show free rotation around both bonds? A) C = O and N - C B) C = O and N - Cn C) Cα - C ... [Show More] and N - Cα D) N - C and Cα - C E) N - Cα and N - C D) N - C and Cα - C Thr and/or Leu residues tend to disrupt an α helix when they occur next to each other in a protein because: A) Steric hindrance occurs between the bulky The side chains B) An amino acid like Thr is highly hydrophobic C) Covalent interactions may occur between the Thr side chains D) Electrostatic repulsion occurs between the Thr side chains E) The R group of Thr can form a hydrogen bond A) Steric hindrance occurs between the bulky The side chains The α-keratin chains indicated by the diagram below have undergone one chemical step. To alter the shape of the α-keratin chains -- as in hair waving -- what subsequent steps are required? A) Chemical oxidation and then shape remodeling B) Shape remodeling and then chemical oxidation C) Chemical reduction and then chemical oxidation D) Chemical reduction and then shape remodeling E) Shape remodeling and then chemical reduction B) Shape remodeling and chemical oxidation Determining the precise spacing of atoms within a large protein is possible only through the use of: A) X-ray diffraction B) Electron Microscopy C) Light Microscopy D) Molecular model building E) Ramachandran plots A) X-ray diffraction Which of the following is LEAST likely to result in protein denaturation? A) Altering net charge by changing pH B) Disruption of weak interactions by boiling C) Changing the salt concentration D) Exposure to detergents E) Micing with organic solvents such as acetone B) Changing the salt concentration Protein S will fold into its native conformation only when protein Q is also present in the solution. However, protein Q can fold into its native conformation without protein S. Protein Q, therefore, may function as a ____________ for protein S. A) Ligand B) Protein Precursor C) Molecular chaperone D) Structural Motif E) Super secondary structural unit C) Molecular chaperone Which of the following statements concerning proteins is true? A) They are a form of secondary structure B) They are examples of structural motifs C) They consist of separate polypeptide chains (subunits) D) They have been found only in prokaryotic proteins E) They may retain their correct shape even when separated from the rest of the protein E) They may retain their correct shape even when separated from the rest of the protein What important function do molecular chaperones perform? A) Assemble protein subunits into quaternary structure B) Transport proteins to either the plasma membrane or release them from cells to the extracellular space C) Add cofactors, coenzymes, or prosthetic groups to proteins as they are synthesized D) Move proteins from endoplasmic reticulum to the Golgi Apparatus E) Fold proteins into native conformation E) Fold proteins into native conformation In most cases, protein folding is complex and inhibited by aggregation. Which statement is FALSE regarding protein folding? A) As ΔS increases, ΔG increases B) Chaperones of the heat shock classes do not promote folding, but rather inhibit aggregation C) Enzymes promote the formation of proper disulfide linkages by eliminating improper folding D) All proteins require the input of energy and the assistance of chaperones for folding E) Secondary structures usually form first in fold D) All proteins require the input of energy and the assistance of chaperones for folding What is false when talking about the MOST important factor that drives the formation of secondary structure of proteins? A) Hydrophobic residues are largely buried in the protein interior B) The number of hydrogen bonds are maximized C) The number of ionic interactions are maximized D) The number of disulfide bonds are maximized D) The number of disulfide bonds are maximized Which statement is FALSE about silk? A) Fibroin is the main protein in silk B) Make from different antiparallel β sheet structures C) Make from different α sheet structures D) Structure is stabilized by: H bonding and London forces E) Small size change (Ala and Gly) allow the close packing of sheets C) Make from different α sheet structures The interactions of ligands with proteins: A) are relatively nonspecific. B) are relatively rare in biological systems. C) are usually irreversible. D) are usually transient. E) usually result in the inactivation of the proteins. D) are usually transient. In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as: A) hyperbolic. B) linear with a negative slope. C) linear with a positive slope. D) random. E) sigmoidal. A) hyperbolic. A D-amino acid would interrupt a α helix made of L-amino acids. Another naturally occurring hindrance to the formation of an α helix in the presences of: A) a negatively charged Arg residue B) a non polar residue near the carboxyl terminus C) a positively charged Lys residue D) a Pro residue E) two Ala residues side by side D) a Pro residue Which of the following best represents the backbone arrangement of two peptide bonds? A) Cα - N - Cα - C - Cα - N - Cα - C B) Cα - N - C - C - N - Cα C) C - N - Cα - Cα - C - N D) Cα - Cα - C - N - Cα - Cα - C E) Cα - C - N - Cα - C - N E) Cα—C—N—Cα—C—N Linus Pauling and Robert Corey found that the CON bond in the peptide link is intermediate in length (1.32 A) between a typical C-N single bond (1.49 A) and a C=N double bond (1.27A). They also found that the peptide bond is planar (al four atoms attached to the C-N group are located in the same plane) and that the two α-carbon atoms attached to the C-N are always trans to each other (on opposite sides of the peptide bond) A) What does the length of the C-N bond in the peptide linkage indicate about its STRENGTH (comparing to the bond strength of the double bond and single bond) and its BOND ORDER (whether it is single, double, or triple) The length of the C - N bond has an intermediate strength. It is not long enough to be a double bond or short enough to be a single bond. It is neither a single or double bond because of its resonance structure. It is not as weak as a single but not as strong as a double bond (it is intermediate). Bond order and bond length indicate the type and strength of covalent bonds between atoms. Bond order and length are inversely proportional to each other: when the bond order is increased, length order is increased. Linus Pauling and Robert Corey found that the CON bond in the peptide link is intermediate in length (1.32 A) between a typical C-N single bond (1.49 A) and a C=N double bond (1.27A). They also found that the peptide bond is planar (al four atoms attached to the C-N group are located in the same plane) and that the two α-carbon atoms attached to the C-N are always trans to each other (on opposite sides of the peptide bond) B) What do the observations of Pauling and Corey tell us about the ease of rotation about the C-N peptide bond? The bond is unable to rotate. Single bonds will rotate while double bonds do not rotate. While this is an intermediate bond, no rotation will occur as it is not quite a single bond. This is important because there is no rotation around the bond which will restrict the ability of it to fold and change its conformation. Our growing understanding of how proteins fold allows researchers to make predictions about protein structure based on primary amino acid sequence data. Consider the following amino acid sequence: Ile-Ala-His-Thr-Tyr-Gly-Pro-Phe-Glu-Ala-Ala-Met-Cys-Lys-Trp-Glu-Ala-Gln-Pro-Asp-Gly-Met-Glu-Cys-Ala-Phe-His-Arg A) Where might bends or B turns occur? The bend will occur between 5-8: Tyr - Gly - Pro - Phe This is because Gly - Pro are next to each other. This occurs primarily in areas with Beta turns (usually in groups of 4) Our growing understanding of how proteins fold allows researchers to make predictions about protein structure based on primary amino acid sequence data. Consider the following amino acid sequence: Ile-Ala-His-Thr-Tyr-Gly-Pro-Phe-Glu-Ala-Ala-Met-Cys-Lys-Trp-Glu-Ala-Gln-Pro-Asp-Gly-Met-Glu-Cys-Ala-Phe-His-Arg B) Where might different intra chain disulfide cross-linkages be formed? Intra-chain disulfide cross linkages might be formed between 13 Cys and 24 Cys. They form between the two cystines. The R-group of the cystine makes the covalent bonds. Our growing understanding of how proteins fold allows researchers to make predictions about protein structure based on primary amino acid sequence data. Consider the following amino acid sequence: Ile-Ala-His-Thr-Tyr-Gly-Pro-Phe-Glu-Ala-Ala-Met-Cys-Lys-Trp-Glu-Ala-Gln-Pro-Asp-Gly-Met-Glu-Cys-Ala-Phe-His-Arg C) Assuming that this sequence is part of a larger globular protein, indicate the probable location (the external surface or interior of the protein) of the following amino acid residues: Asp, Ice, Ala, Gln, Lys. The outer protein surface is polar while the interior of the protein is non-polar (due to the hydrophobic effect). These residues are non polar as the majority are non polar: Asp (-) Ile (non-polar) Thr (polar) Ala (non-polar) Glu (polar) Lys (+) There are more hydrophilic residues than hydrophobic residues making this non-polar on the EXTERIOR SURFACE. Protein A has a binding site for ligand X with a KD of 10-6 M. Protein B has a binding site for ligand X with a KD of 10-9 M A) Which protein has a higher affinity for ligand X and why? P(A): Kd = 10-6 M P(B): Kd = 10-9 M Since protein A is larger than protein B, protein A has a higher kd value than protein B. Therefore, Protein B has a higher infinity due to the inverse relationship of affinity and kd value. Protein A has a binding site for ligand X with a KD of 10-6 M. Protein B has a binding site for ligand X with a KD of 10-9 MB) Convert KD to KA for both proteins. Kd and affinity have an inverse reaction, so a smaller kd = high affinity. This inverse relationship will allow us to use the equation: P(A) Ka 1/10^-6 = 10^6 P(B) Ka 1/10^-9 = 10^9 What is the effect of the following changes on the O2 affinity of hemoglobin? A) A drop in the pH of blood plasma to 7.4 - 7.2 Decrease What is the effect of the following changes on the O2 affinity of hemoglobin? B) An increase in the pH from 7.4 to 7.6 increase What is the effect of the following changes on the O2 affinity of hemoglobin? C) A decrease in the partial pressure of CO2 in the lungs from 6kPa (holding one's breath) to 2 kPa (normal). Increases As the pH drops, the O2 affinity also drops What is the effect of the following changes on the O2 affinity of hemoglobin? D) An increase in the BPG level from 5mM (normal altitudes) to 8mM (high altitudes). Decreases As the BPG levels increase, the O2 affinity decreases. What is the effect of the following changes on the O2 affinity of hemoglobin? An increase in CO from 1.0 parts per million in a normal indoor atmosphere to 30 ppm in a home that has a malfunctioning or leaking furnace Decreases As the CO concentration increases, the O2 affinity of hemoglobin decreases and that of CO affinity of hemoglobin increases. Three membrane receptor proteins bind tightly to a hormone. Based on the data in the table below, A) what is the Kd for hormone binding by protein 2 The Kd for hormone binding by protein 2 is ~0.5nM Three membrane receptor proteins bind tightly to a hormone. Based on the data in the table below, B) Which of these proteins bind most tightly to this hormone? Protein 2 will bind most tightly to this hormone. The less dissociation, the stronger the binding between a molecule and its ligand. Since protein 2 has the least kd, it is stronger than the other two proteins. [Show Less]
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